This is largely inherited from 5e, yeah. Eldritch Knight and Arcane Trickster
are INT-casters, but they're very much Fighter/Rogues first and tend to be best off using their spells for support. There's also the Artificer now, of course, but that doesn't look like it's coming to
Baldur's Gate 3. I'll note that Ranger is also a Wisdom half-caster and the yet-unreleased Monk usually depends on having both high Dexterity and Wisdom -- so it's not quite Charisma unambiguously outclassing all the mental stats. (Wisdom also has some general niceties regardless of class: Perception tends to be valuable, and Wisdom saves are a lot more common than INT/CHA ones.)
But all this does leave Intelligence largely the domain of the Wizard, though: it doesn't really have many applications beyond INT checks and saves, and INT saves are on the rarer end. Mostly to see through illusions and to resist mind flayers, from what I remember -- which, hey, at least on paper mind flayers should be popping up. In principle, it could be interesting to see Intelligence given a bit more use: if you were able to apply your knowledge to resolve a few conflicts or glean something extra (beyond flavour). I can't really think of many in-game examples there right now.
One related fun fact, though: the initial intention in 5e was to use Intelligence
for Warlock spells. I don't mind them keying off Charisma, but I think it comes across when you read their class description and see them described as "seekers of knowledge" and "delvers into secrets". If they had, there'd be two casters per stat -- although Warlocks use Pact Magic rather than being traditional full-casters.
